What absorbs at 1638 cm⁻¹ in an FTIR spectrum?
A band near 1638 cm⁻¹ can point to several functional groups. Below are the most likely assignments, ranked by how much published evidence supports each — every one traceable to literature (DOI) and cross-validated against our 130,000+ reference spectra and knowledge graph.
Backed by 8 cited sources
Possible functional-group assignments
| Functional group | Supporting facts | Cited sources | Top confidence |
|---|---|---|---|
| Alkene (C=C) | 18 | 17 | 1.0 |
| Carbonyl (C=O) | 7 | 6 | 0.9 |
| Water (H2O) | 4 | 4 | 1.0 |
| Alkyl C-H | 4 | 4 | 0.9 |
| Aromatic ring | 4 | 4 | 0.9 |
| Amide | 3 | 3 | 0.9 |
| Carboxyl (COOH) | 2 | 2 | 0.9 |
| Methacrylate | 2 | 2 | 0.9 |
| Protein beta sheet | 2 | 1 | 0.9 |
| Quinone | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 0.9 |
| Ammonium | 1 | 1 | 0.9 |
| C c single bond | 1 | 1 | 0.7 |
Ranking reflects accumulated literature evidence, not a single authoritative rule. Always confirm against your sample context.
Literature behind these assignments
-
Alkene (C=C) confidence 1.0
“Explicit assignment in text.”
Rastelli 等 - 2008 - Degree of Conversion and Temperature Increase of a DOI: 10.1134/S1054660X0812030X -
Alkene (C=C) confidence 1.0
“Explicit assignment: 'aliphatic C=C (peak at 1638 cm-1)'”
Rastelli 等 - 2008 - Effect of power densities and irradiation times on DOI: 10.1134/S1054660X08090132 -
Alkene (C=C) confidence 1.0
“Explicit assignment: '3rd peak (1638.15 cm-1) belongs to C=C'.”
Tasci 等 - 2016 - Determination of alliin and allicin in the plant o DOI: 10.17660/ActaHortic.2016.1143.19 -
Quinone confidence 1.0
“explicit assignment in text”
Adiani 等 - 2020 - Microbial quality assessment of minimally processe DOI: 10.1038/s41598-020-62895-y -
Water (H2O) confidence 1.0
“H2O bending vibrations”
Krishnamurithy 等 - 2019 - The physicochemical and biomechanical profile of f DOI: 10.1371/journal. -
Alkene (C=C) confidence 1.0
“Explicit assignment in text: 'aliphatic C=C peak at 1638 cm-1'”
Yan 等 - 2010 - Changes in Degree of Conversion and Microhardness DOI: 10.2341/09-174-L -
Alkene (C=C) confidence 0.95
“Peak at 1638 cm-1 assigned to aliphatic carbon-carbon double bond.”
Lopes 等 - 2022 - Development of an Antibacterial Dentin Adhesive DOI: 10.3390/polym14122502 -
Alkene (C=C) confidence 0.95
“Explicit assignment: 'peak at 1638 ascribed to C=C'”
Rajczak 等 - 2020 - Preparation and Characterization of UV-Curable Acr DOI: 10.3390/polym12020358
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